The present invention is concerned with a method for fault location on series compensated power transmission lines with two-end unsynchronized measurement, finding an application in the electrical power sector and for overhead transmission lines uncompensated and with series compensation.
The location fault technique on series compensated power transmission lines is known from EP1051632B1. In this solution it has been proposed to calculate distance to fault with utilizing local measurements from one terminal of the series compensated transmission line where fault locator is placed. This method makes use of transforming the parallel connection of series capacitor and metal oxide varistor (MOV) into a model—equivalent impedance in the form of a series connection of resistance and reactance, both fundamental current magnitude dependent. This equivalent impedance is used to calculate the distance to fault. This method requires the knowledge of the parameters of series capacitor banks and MOV elements as well.
A method of reach measurement for distance relay and fault locators for series—compensated transmission lines is know from U.S. Pat. No. 6,336,059 B1. In the method according to that invention the fault location estimation is done with using local information only. In the method a number of line currents samples are measured, where such samples are representative of values of line current waveform at successive instants of time on the series compensation line. Capacitor voltage values are computed based on measured currents in accordance with an equation which takes into account the non-linear protection device—metal oxide varistor parallel to the installed series capacitor. The distance to fault is calculated with taking into account the calculated earlier capacitor voltage values.
In US patent 2006/0142964 A1 it is presented the fault location method with using two end currents and voltages measurement. The invention is characterised in that after determination of current transformer saturation at first end of the line A or second end B, the distance to fault is calculated with using voltage from both ends of the line and currents only from this side of the line where current transformers are not saturated. Calculation of distance to fault is done based on generalized fault loop model. In this model the total fault current is determined with use of lumped line model and, one end current signals and two ends voltage signals. However the method according to the cited invention is not designed for locating faults on series compensated lines.
Another method of fault location on series compensation lines with using two-end measurements is known from the article Chi-Shan Yu, Chih-Wen Liu, Sun-Li Yu, and Joe-Air Jiang, “A New PMU-Based Fault Location Algorithm for Series Compensated Lines”, IEEE Transactions on Power Delivery, VOL. 17, NO. 1, JANUARY 2002, pp. 33-46. This method uses voltage and current signals measured synchronously at both ends of a single series compensated line. Thus, differs by the kind of measurement (synchronous measurement) and type of a line (single series-compensated line) from the invented approach, which is designed for use of more general case of asynchronous measurements and in application to both single and double-circuit uncompensated and series-compensated lines. Moreover, the cited approach does not provide an analytic formula for the sought distance to fault but is based on scanning along the whole line section for finding the fault position at which the determined fault voltage and total fault current are in phase (this is so since the fault path has the resistive character). For each checked point on the line, the fault voltage and total fault current have to be determined from the symmetrical components of current and voltage. This imposes high computational burden required for performing the fault location. In contrast, the invented approach delivers the compact formula for the sought distance to fault, derived with strict considering the distributed parameter model of the line.
From the article Claude Fecteau “Accurate Fault Location Algorithm for Series Compensated Lines Using Two-Terminal Unsynchronized Measurements and Hydro-Quebec's Field Experience”, presented to the 33-rd Annual Western Protective Relay Conference, Spokane, Wash., Oct. 17-10, 2006 Conference there is known the solution that is to a certain extent related with the invented approach. One can point out that the developed approach is more general (single and double-circuit lines, uncompensated and series-compensated lines). The cited approach does not provide an analytic formula for the sought distance to fault. Instead, the distance to fault is determined iteratively by minimizing the objective function for the reactance of the fault impedance. This imposes higher computational burden than the invented approach.
Moreover, the invented approach offers additionally determination of the synchronization angle, in case of single phase-to-ground faults and phase-to-phase faults (majority of the faults in practice), with use of the post-fault quantities. This is advantageous from the assuring precise synchronization point of view.